Vacuum-type circuit interrupter having a stroke length dependent upon current magnitude

ABSTRACT

Discloses a vacuum-type circuit interrupter comprising currentresponsive means for varying its opening stroke length in accordance with the magnitude of the current being interrupted.

United States Patent Philip Barltan Media, Pa.

Feb. 3, 1969 June 1, 1971 General Electric Company lnvcmor Appl. No.Filed Patented Assignee VACUUM-TYPE CIRCUIT INTERRUPTER HAVING A STROKELENGTH DEPENDENT UPON CURRENT MAGNITUDE 5 Claims, 5 Drawing Figs.

US. Cl 200/144, 335/40, 200/153 Int. Cl 1101b 33/66 Field ofSearch335/16, 40, l74;200/147 C, 144.2, 148,153.20

[56] References Cited UNITED STATES PATENTS 3,050,073 10/1961 Reiss eta1 200/147(C)X 3,164,700 1/1965 Bodenschatz 200/147(C)X 3,418,43912/1968 Casey et al ZOO/144(2) 3,492,609 1/1970 Murai et a1. 335/16Primary Examiner-Robert K. Schaefer Assistant EgcaminerRobert A.Vanderhye Attorneys-J Wesley l-laubner, William Freedman, Frank L.

Neuhauser, Oscar B. Waddell and Melvin M. Goldenberg ABSTRACT: Disclosesa vacuum-type circuit interrupter comprising current-responsive meansfor varying its opening stroke length in accordance with the magnitudeof the current being interrupted.

/NVENTOR.' PH/L/P BAR/(AN,

ATTORNEY PATENVTED JUN 1 an SHEET 2 OF 2 PHASEM' nvvmvron PHIL/P BAR/(AN,

ATTORNEY VACUUM-TYPE CIRCUIT INTERRUPTER HAVING A STROKE LENGTHDEPENDENT UPON CURRENT MAGNITUDE This invention relates to a vacuum-typecircuit interrupter and, more particularly, to a vacuum-type interrupterwhich has a stroke length dependent upon the magnitude of the currentbeing interrupted.

When used in highly repetitive duty-switching applications, such as inmotor control contactors, a vacuum interrupter must have an extremelylong life, e.g., hundreds of thousands or even millions of operations.An important determinant of the life of a vacuum interrupter is the lifeof its bellows. The bellows is a flexible metal part that forms avacuumtight seal between the movable contact rod and the evacuatedenvelope of the vacuum interrupter. Each time the interrupter is openedor closed, this bellows is flexed; and after many such opera tions, maydevelop, through fatigue, a crack which allows leakage into theevacuated envelope.

If the stroke of the vacuum interrupter used in such switchingapplications can be kept short, a much higher number of operations canbe endured before any fatigue induced cracks will develop in thebellows. But there is one consideration which limits the extent to whichthe stroke can be shortened, and that is the short circuit currentinterrupting ability of the interrupter. In the vast majority ofoperations,

only relatively light currents will be interrupted by the interrupter;but occasionally the interrupter will be called upon to interrupt ashort circuit current, which has a much higher magnitude. These latterinterruptions require a considerably longer stroke than the lightcurrent typically interrupted, and the interrupter would be unable tohandle such currents if its stroke were limited to the short length thatis ideal for prolonged bellows life.

An object of my invention is to maintain the stroke of such a vacuuminterrupter short in length so as to prolong the life of its bellows,yet without defeating the ability of the interrupter to handleoccasional short circuit currents.

Another type of switching application that I am concerned with is thatin which the vacuum interrupter is used in an infrequently operatedprotective circuit breaker that is relied upon for short circuitinterrupting duty and for capacitance switching duty. For capacitanceswitching duty, it has been found that a longer stroke is needed thanthat which is optimum for short circuit current interruption. Thislonger stroke helps the interrupter to successfully withstand the highervoltages that are imposed by capacitance switching. But surprisingly,this longer stroke detracts from the short circuit current interruptingability of the vacuum interrupter.

Accordingly, another object of my invention is to provide in aprotective circuit breaker a vacuum interrupter which can develop astroke long enough to perform well during capacitance switchingoperations, yet without impairing its ability to interrupt short circuitcurrents.

In carrying out the invention in one form, I provide a vacuuminterrupter which has means for automatically changing the length of itsstroke in accordance with the magnitude of the current beinginterrupted. In the first switching application referred to above, i.e.,the repetitive duty application, I provide the interrupter with twostops, one of which is capable of limiting the stroke length to a shortvalue that is especially suited for prolonged bellows life and the otherof which is capable of limiting the stroke length to a longer valueappropriate for short circuit interruptions. Under light currentinterrupting conditions, the first stop controls the stroke length; butcurrent responsive means is provided which acts under high currentconditions to disable the first stop and allow the second stop tocontrol the stroke length.

In the second switching application referred to above, i.e., theprotective circuit breaker application, first and second stops ofasimilar character to those referred to in the previous paragraph areprovided; but the first stop is normally disabled and the second stopnormally controls the stroke length. Under high current conditions,however, current res onsive means frees the first stop from itsdisability and allows it to control, thus reducing the stroke length.

For a better understanding of the invention, reference may be had to thefollowing description taken in conjunction with the accompanyingdrawings, wherein:

FIG. I is a sectional view partly in section showing a vacuuminterrupter embodying one form of my invention.

FIG. 2 is a sectional view along the line 2-2 of FIG. 1.

FIG. 3 is a schematic showing ofa polyphase circuit breaker comprisingsingle phase intcrrupters such as shown in FIG. 1.

FIG. 4 is a schematic showing of a modified form of the invention.

FIG. 5 is a schematic showing of another modified form of the invention.

Referring now to FIG. 1, there is shown a vacuum-type circuitinterrupter 10 comprising a highly evacuated housing 11 comprising acylindrical insulating case 12 and upper and lower end caps 13 and 14joined to the casing 12 by suitable vacuumtight seals. Mounted withinhousing 11 are two separable contacts 16 and 17, shown in FIG. I intheir engaged, or closed, position. The upper contact 16 is a stationarycontact mounted on a stationary conductive rod 16a that is integrallyjoined to the upper end cap 13. The lower contact 17 is a movablecontact that is mounted on a conductive operating rod 17a that projectsfreely through the lower end cap 14. A I

flexible metallic bellows 18 is joined in sealed relationship at itsrespective opposite ends to rod 17a and end cap 14. This flexiblebellows permits vertical movement of rod without impairment of thevacuum inside housing 11. The vacuum interrupter is mounted on astationary conductive stud 20 by means of a mounting bracket 22 suitablyfixed to stud 20 and lower end cap 14. Bracket 22 carries a bearing 24that surrounds the movable operating rod 17a and guides it for openingand closing movement.

For transmitting opening and closing motion to movable operating rod170, I provide a conductive crossbar 26 pivotally mounted on stationarybracket 22 at 28. Crossbar 26 is rigidly attached at its free end tomovable operating rod 170, and when it is pivoted in a counterclockwisedirection from its position of FIG. I drives the operatingrod'downwardly to separate contacts l7, 16.

For transmitting opening and closing motion to crossbar 26, l provide anactuating lever 30 that is mounted for pivotal motion on stationarypivot 28. A compression-type wipe spring 32 located between lever 30 andcrossbar 26 biases these parts apart. The wipe spring 32 encircles apull rod 34, which is pivotally mounted at 35 on the crossbar 26 andextends freely through an opening in the actuating lever 30. The pullrod 34 has a stop 36 on its lower end that is adapted to be engaged bythe lower side of lever 30 on an opening operation, as will soon bedescribed.

Actuating lever 30 is biased in a clockwise opening direction by atorsion-type opening spring 39. The actuating lever 30 is normallyprevented from moving out of its position of FIG. 1 by a closing rod 40that freely extends through an opening in the actuating lever 30 andcarries a stop 42 against which lever 30 normally bears. For reasonswhich will soon be explained, the connection 41 between the actuatinglever 30 and closing rod 40 is a lost-motion connection. Closing rod 40is latched in its illustrated position by a suitable trip latch (shownat 43 in FIG. 3). When closing rod 40 is released for downward movement,the opening spring 39 and wipe spring 32 drive the actuating lever 30 ina counterclockwise opening direction. After a short amount ofcounterclockwise travel, actuating lever 30 impacts against the stop 36on pull rod 34, and the resulting impact plus force from opening spring39 rapidly drive thepull rod downwardly in the direction of arrow 44(FIG. 1). This downward motion of the pull rod produces counterclockwisemotion of crossbar 26, thereby driving'the operating rod 17a downwardlyto separate the contacts.

Closing is performed after the above-described opening operation bymoving the closing rod 40 in an upward direction, thus driving stop 42against lever 30 to move lever 30 clockwise toward its position of FIG.I. Such a clockwise motion is transmitted to crossbar 26 throughcompression spring 32, thus driving the crossbar 26 clockwise toward itsposition of FIG. I. This clockwise motion of crossbar 26 continues untilthe contacts engage. Clockwise motion of actuating lever 30 continuesfor a short additional travel after the contacts engage, therebypartially compressing the wipe spring 32. This additional travel, whichcompresses spring 32, is referred to as contact wipe. At the end ofaclosing stroke, latch 43 of FIG. 3 resets and holds the closing rod 40in its elevated position of FIG. I.

For carrying current between the stud 20 and conductive operating rod170 I provide a short length of conductive braid 50. This braid hasferrules at both ends, one of which is joined to the stud 20 and theother of which is joined to operating rod 17a via crossbar 26. The braidmay be thought of as being ofa generally L-shape. Current through thebreaker, when it is in the closed position shown, follows a pathdepicted by the dotted line arrows 54. This path extends from stud 20through parts 50, 26, 17a, l7, l6. and 16a to the upper terminal 55 ofthe breaker.

For controlling the length of the opening stroke of the vacuuminterrupter, I provide two stops 60 and 62. The first stop 60 is amovable stop which normally predominates in controlling the strokelength. This stop 60 can be disabled, as will soon be described, toallow the second stop 62 to control. The second stop 62 is a fixed stopthat is rigidly secured (by means not shown) to the stationary bracket22.

The first stop 60 is a lever of magnetizable material that is pivotallymounted on a fulcrum 65 secured to bracket 22. The lever 60 is normallymaintained in its position of FIG. I by a reset spring 68 which biaseslever 60 counterclockwise into its effective position shown. When thestop lever 60 is in its effective position of FIG. I, it will engage theouter end portion of the crossbar 26 when the crossbar enters its dottedline position 70 during an opening operation, thereby limiting theopening stroke to a relatively small value.

When the current through the interrupter exceeds a predetermined value,the stop 60 is rapidly withdrawn from its effective position of FIG. Iand thus is rendered ineffective to control the opening stroke. Thispermits the vacuum interrupter to have a longer stroke inasmuch as thecrossbar 26, during its opening travel, will now be able to move pastthe dotted line position 70 into a position of greater contactseparation, where it will encounter the second stop 62.

For withdrawing the stop lever 60 in response to high current throughthe interrupter, I provide a U-shaped magnetic core 72 that partiallysurrounds the conductive braid 50 and is fixed to the stud 20. When thecurrent through the braid 50 exceeds a predetermined value, there is ahigh enough attractive force between the core 72 and the stop lever 60to drive the stop lever counterclockwise about its pivot 65 intoengagement with the end faces 75 f the magnetic core. The current levelat which this motion of the stop lever 60 takes place is determined bythe size of reset spring 68. In one embodiment of the invention, thereset spring is of such a size that this motion occurs only when acurrent of short circuit magnitude passes through braid 50.

The interrupter of FIG. I is especially adapted for highly repetitiveswitching applications, where the required life span of the interruptertypically is many hundreds of thousands of operations. As pointed outhereinabove, an important determinant of the life span of suchinterrupter is the life of its bellows. Each time the interrupter opensor closes, this bellows is flexed, and this subjects the bellows torepeated stresses which, through fatigue, can ultimately cause cracks todevelop in the bellows.

For reducing the severity of these stresses, thus prolonging the bellowslife, I normally limit the stroke of the vacuum interrupter to arelatively short value. This is done with the first stop 60, as abovedescribed. This short stroke is adequate for the vast majority of theswitching operations inasmuch as these involve only relatively lightcurrent, which can be interrupted with a short stroke. Occasionally,however, it will be necessary to interrupt short circuit currents, andthis will require a longer stroke to insure successful interruption.

By quickly disabling the first stop 60 in response to short circuitcurrents, thus allowing the second stop 62 to control, I am able toprovide the necessary increased stroke length needed for interruptingshort circuit currents. When the interrupter is closed following a shortcircuit current interruption, the reset spring 68 quickly returns thestop 60 to its effective position of FIG. 1, thus once again restoringthe short stroke for normal interrupting operations.

A feature of some significance is that my stroke varying means can beused in a polyphase circuit breaker to change the stroke length of theinterrupter in one phase without affecting the stroke length of theinterrupters in the other phases. This will be apparent from theschematic diagram of FIG. 3. Here the closing rods that extend to theinterrupters of each phase are designated 40, 40a and 40b. The actuatinglevers for the respective phases are designated 30, 30a and 30b. Alost-motion connection 41, 4111 or 41b is present between each of theseactuating levers and its associated closing rodv The actuating leversare coupled to the interrupters in the respective phases by pull rods34, 34a and 34b. The actuating levers are respectively biased in acounterclockwise opening direction by opening springs 39, 39a and 39b,but are normally prevented from so moving by shoulders 42, 42a and 42bon their associated closing rods. Parts 30, 34, and 39-42 are theidentically designated parts of FIG. 1. Their counterparts in the othertwo phases bear the same reference nu merals but with the suffixes a orb." Each of the closing rods 40, 40a, 40b is pivotally connected at itslower end to a crank I00, a or 100b, which, in turn, is keyed to arotatably mounted shaft 104 common to all three phases and tying thecranks together. Crank 100 has a downwardly projecting arm that carriesa latch roller 106 cooperating with a trip latch 43 common to all threephases. When trip latch 43 is in a position of FIG. 3, the roller I06bears against latch 43, thereby holding all the parts in their closedposition of FIG. I. When latch 43 is tripped by a tripping solenoid 108,the cranks I00, 100a and l00b are free to move in a clockwise openingdirection. The opening springs 39, 39a, 39b respond by driving therespective actuating levers 30, 30a, and 30b in a counterclockwiseopening direction, thus opening the interrupters in the three phases.Stops 60 and 62, corresponding to stops with the same reference numeralsin FIG. 1, determine the length of the opening stroke in phase I.Similar stops with corresponding reference numerals determine the lengthof the opening stroke in each of the other phases.

It will be apparent that the length of the opening stroke in any onephase will be determined by the stops in that particular phase and willnot be affected by the stops in the other phases. For example, if it isassumed that short-stroke stop 60 of phase I has been disabled, then thestroke in phase I will be determined by stop 62 and will be relativelylong. If the short stroke stops 60a and 60b in the other two phases arestill operative, they will determine the stroke in these particularphases, and accordingly the stroke in these phases will be relativelyshort. The lost motion connection 41, 41a or 41b between each actuatinglever and its closing rod allows the actuating lever to be blocked in agiven phase by the shortstroke stop in that phase without interferingwith the continued opening movement of the closing rods in the otherphases.

The polyphase arrangement of FIG. 3 readily accommodates a circuitcondition where short circuit current might flow through one of thephases of the circuit while the other phases are carrying normal lowcurrents. In response to such a condition, the stroke-control means ofthe phase carrying short circuit current disables its short-stroke stop60, allowing a long stroke in that phase, thus permitting effectiveinterruption of the high current therein. The interrupters of the otherphases, which are seeing low current, do not need the long stroke andoperate with their usual short stroke.

At the end of such an opening operation, cranks 100, 100a and 100!) willbe in their dotted line position of FIG. 3. A closing roller I12 carriedby crank 100 will be located adjacent the armature of a closing solenoid114. Closing of the threephase circuit breaker is affected by operatingsolenoid 114 to lift its armature and return closing roller 112 to itssolid line position. This returns the three cranks I00, 100a and 1001;to their solid line positions of FIG. 3, simultaneously lifting rods 40,40a and 40b through a closing stroke. During this closing stroke, theactuating lever 30, which had previously moved through a long openingstroke will first be picked up by its closing rod 40; and afteradditional closing travel, the other actuating levers 30a and 30b, whichhad moved through short operating strokes, will be picked up by theirrespective closing rods 40a and 40b. The movable contacts of theinterrupters in all three phases reach their closed position atsubstantially the same time.

Another type of switching application that I am concerned with is one inwhich the vacuum interrupter is used in a protective circuit breakerthat is relied upon for short circuit interrupting duty and capacitanceswitching duty. For capacitance switching duty, it has been found that alonger stroke is needed than that which is optimum for short circuitinterruptions. This longer stroke helps to withstand the higher voltagesthat are imposed by capacitance switching duty; but, surprisingly, itdetracts from the short circuit current interrupting capability.

FIG. 4 shows a circuit breaker which can provide a shorter stroke undershort circuit interrupting conditions than under capacitance switchingconditions. In passing, it should be noted that this short stroke inFIG. 4 corresponds to the long stroke in FIG. 1, whereas the long strokein FIG. 4 is of still greater length. The circuit breaker of FIG. 4comprises a vacuum interrupter which is substantially the same as thatof FIG. 1 and thus has its parts designated by corresponding referencenumerals. In addition, the interrupter of FIG. 4 is provided with anopening spring 80 which drives the movable contact 17 downwardly whenreleased by a trip latch 82. The trip latch 82 is operable by solenoid83 which is connected in a trip circuit 85. Trip circuit 85 can becompleted either by a manually controlled switch 86 or a switch 88 whichis operated to closed position by suitable means (not shown) responsiveto overcurrent in the circuit through the interrupter. Completion oftrip circuit 85 operates the tripping solenoid 83 to release latch 82,thus allowing opening spring 80 to drive the movable contact 17 downwardthrough an opening stroke.

The length of the opening stroke is determined by either one of twostops 90 and 91. Stop 91 is a stationary stop disposed in the path ofthe movable contact operating rod 17a. Under low current conditions,this stop 91 will determine the length of the opening stroke. This stopis so located that it permits a relatively long opening stroke beforebeing engaged by operating rod 17a. Since capacitance switchingoperations are low current interruptions, a relatively long stroke willbe provided for capacitance switching, thus facilitating suchoperatrons.

The other stop 90 is normally inactive, but it is brought into operationin response to a high current through the interrupter. This stop 90 iscontrolled by solenoid 93 that has its coil 94 connected in series withcircuit 92 through the interrupter. A reset spring 95 normally maintainsthe stop 90 in its inactive position. When current exceeding apredetermined magnitude passes through the circuit 92, solenoid 93responds by quickly driving the stop 90 into its dotted line position.This occurs before actual opening movement of the movable contactoperating rod 17a begins. Accordingly, when movable contact operatingrod 17 moves downwardly during an immediately following high currentopening operation, it encounters stop 90 and is thus prevented frommoving through its full opening stroke. Solenoid reset spring 95 is ofsuch a size that the stop 90 is made operative for currents of shortcircuit magnitude. Thus under short circuit interrupting conditions, thedesired shorter stroke is provided.

After an interrupting operation, the solenoid 93 will be deenergized.During the early stages of a subsequent closing operation, the resetspring 95 will restore the stop to its ineffective position as soon asthe operating member lifts it off the stop 90 to free it for resetmotion.

During low current interruptions, solenoid 93 will be ineffective tomove stop 90 into its effective position. Thus, during low currentinterruptions, the movable contact can quickly move through its desiredrelatively long stroke without any interference from stop 90.

FIG. 5 shows a modification of the general arrangement shown in FIG. 4.Here the stop 90 is biased toward its effective position by a spring 96that is normally prevented from moving stop 90 into its effectiveposition by a latch 97 controlled by a solenoid 98 connected in serieswith the circuit 92 through the interrupter. When current of shortcircuit magnitude flows through circuit 92, the solenoid 98 operates itslatch 97, thus permitting spring 96 to drive the stop 90 into itseffective position where it is can provide the desired reduction instroke length.

A reset member 99, attached to operating rod 17a, is used for returningstop 90 to its normal position when the operating rod 17a is lifted (bysuitable closing means, not shown) during a closing operation. Thisreset member 99 will prevent the stop from being operated during anopening operation prior to initial contact movement. But immediatelyfollowing initial contact movement, reset member 94 moves out of the wayof stop 90, allowing stop 90 to immediately move into its effectiveposition if it has been released to do so by solenoid 98.

It is to be understood that the three-phase arrangement of FIG. 3 can beused in either of the above two switching applications. Whether theshort-stroke stop (60 of FIG. 3) is normally active (as in FIG. 1) ornormally inactive (as inFIGS. 4 8L 5), there is still independencebetween the interrupters in the various phases as a result of thelost-motion connections 4!, 41a, 41b. Thus, the stroke-control means ineach phase can change the stroke length in that phase in response tocurrent therethrough without affecting the stroke length in the otherphases. One type of switching duty where this ability is important to acircuit breaker is that involved when the circuit breaker is performinga line-dropping operation on two phases and is interrupting a shortcircuit current on the remaining phase. The line-dropping operation is alight current capacitance switching operation, and the interrupters inthese phases retain their relatively long stroke since their associatedstops 90 of FIG. 4 or 5 remain inactive. But the interrupter in theshort-circuited phase has a reduced length stroke (as a result of itsassociated stop 90 being activated), which facilitates interruption ofthe short circuit current.

While I have shown and described particular embodiments of my invention,it will be obvious to those skilled in the art that various changes andmodifications may be made without departing from my invention in itsbroader aspects; and I, therefore, intend in the appended claims tocover all such changes and modifications as fall within the true spiritand scope of my invention.

lclaim:

1. A vacuum-type circuit interrupter for highly repetitive switchingduty comprising:

a. a highly evacuated housing,

b. a pair of relatively movable contacts within ,said housing that havea position of engagement,

c. an operating member projecting into said housing from the exteriorthereof and coupled to one of said contacts,

d. means comprising said operating member for moving said one contactthrough an opening stroke that separates said contacts and interruptsthe circuit therethrough,

e. a flexible metal bellows providing a vacuumtight seal between saidoperating member and said housing,

f. and stroke-length control means responsive to current through saidcontacts for varying the length of said open ing stroke in accordancewith the magnitude of said current, said stroke-length control meanscausing the length of said opening stroke to the greater for shortcircuit current interruptions than for light-current interruptions,

thus allowing light-current interruptions to be effected with a reducedflexure of said bellows, said stroke-length control means comprising:

i. a first stop for limiting the opening stroke to a relatively shortlength,

ii. a second stop effective when said first stop is disabled forlimiting the opening stroke to a greater length, and iii.current-sensitive means for disabling said first stop when the currentthrough said contacts exceeds a predetermined value, thereby renderingsaid second stop effective to govern the stroke length.

2. A vacuum-type circuit interrupter for interrupting short circuitcurrents and capacitive currents comprising:

a. a highly evacuated housing,

b. a pair of relatively movable contacts within said housing that have aposition of engagement,

c. an operating member projecting into said housing from the exteriorthereof and coupled to one of said contacts, d. means comprising saidoperating member for moving said one contact through an opening strokethat separates said contacts and interrupts the circuit therethrough,

c. a flexible metal bellows providing a vacuumtight seal between saidoperating member and said housing,

f. and stroke-length control means responsive to current through saidcontacts for varying the length of said opening stroke in accordancewith the magnitude of said current, said current-responsive controlmeans causing the length of said opening stroke to be greater forlightcurrent interruptions than for heavy current interruptions, thusproviding a stroke of greater length for capacitance switchingoperations than for short circuit current interruptions.

3. A vacuum-type circuit interrupter as defined in claim 2 in which saidstroke-length control means comprises:

a. a first stop that is normally disabled but which is effective uponremoval of said disability to limit said opening stroke to a relativelyshort value,

b. a second stop that limits said opening stroke to a greater lengthwhen said first stop is disabled,

c. and current-sensitive means for removing said disability when thecurrent through said contacts exceeds a predetermined value, therebyrendering said first stop effective to govern the stroke length on shortcircuit current interruptions.

4. In a polyphase vacuum circuit breaker comprising a plurality ofvacuum interrupters for the respective phases of the circuit, eachvacuum interrupter comprising:

a. a highly evacuated housing,

b. a pair of relatively movable contacts within said housing that have aposition of engagement,

c. an operating member projecting into said housing from the exteriorthereof and coupled to one of said contacts, d. means comprising saidoperating member for moving said one contact through an opening strokethat separates said contacts and interrupts the circuit therethrough,

e. a flexible metal bellows providing a vacuumtight seal between saidoperating member and said housing,

f. and stroke-length control means responsive to current through saidcontacts for varying the length of said opening stroke in accordancewith the magnitude of said current, the stroke-length control means ofeach phase being operable independently of the stroke-length controlmeans of the other phases for varying the stroke length of theinterrupter in any one phase in accordance with the current in thatphase without affecting the stroke length in the other phases.

5. In a polyphase vacuum circuit breaker comprising a plurality ofvacuum interrupters for the respective phases of the circuit, eachvacuum interrupter comprising:

a'. a highly evacuated housing,

b. a pair of relatively movable contacts within said housing that have aposition of engagement, c. an operating member pro ecting into saidhousing from the exterior thereof and coupled to one ofsaid contacts,

d. means comprising said operating member for moving said one contactthrough an opening stroke that separates said contacts and interruptsthe circuit therethrough,

e. a flexible metal bellows providing a vacuumtight seal between saidoperating member and said housing,

. and stroke-length control means responsive to current through saidcontacts for varying the length of said opening stroke in accordancewith the magnitude of said current; the combination of:

g. a linkage connected to the interrupters in all phases for impartingclosing motion thereto after an opening operation,

h. latching means for holding said linkage in an operated position aftera closing operation to hold said interrupters closed,

i. said latching means being releasable to permit opening of saidinterrupters,

j. a plurality of opening operators respectively biasing theinterrupters toward open position and operable upon release of saidlatching means to separate the contacts of their respectiveinterrupters, and

k. a lost-motion connection between said linkage and each interrupterwhich allows the opening stroke in the associated interrupter to beterminated at a relatively short value by said stroke-length controlmeans without blocking continued opening travel in the otherinterrupters.

1. A vacuum-type circuit interrupter for highly repetitive switchingduty comprising: a. a highly evacuated housing, b. a pair of relativelymovable contacts within said housing that have a position of engagement,c. an operating member projecting into said housing from the exteriorthereof and coupled to one of said contacts, d. means comprising saidoperating member for moving said one contact through an opening strokethat separates said contacts and interrupts the circuit therethrough, e.a flexible metal bellows providing a vacuumtight seal between saidoperating member and said housing, f. and stroke-length control meansresponsive to current through said contacts for varying the length ofsaid opening stroke in accordance with the magnitude of said current,said strokelength control means causing the length of said openingstroke to the greater for short circuit current interruptions than forlight-current interruptions, thus allowing light-current interruptionsto be effected with a reduced flexure of said bellows, saidstroke-length control means comprising: i. a first stop for limiting theopening stroke to a relatively short length, ii. a second stop effectivewhen said first stop is disabled for limiting the opening stroke to agreater length, and iii. current-sensitive means for disabling saidfirst stop when the current through said contacts exceeds apredetermined value, thereby rendering said second stop effective togovern the stroke length.
 2. A vacuum-type circuit interrupter forinterrupting short circuit currents and capacitive currents comprising:a. a highly evacuated housing, b. a pair of relatively movable contactswithin said housing that have a position of engagement, c. an operatingmember projecting into said housing from the exterior thereof andcoupled to one of said contacts, d. means comprising said operatingmember for moving said one contact through an opening stroke thatseparates said contacts and interrupts the circuit therethrough, E. aflexible metal bellows providing a vacuumtight seal between saidoperating member and said housing, f. and stroke-length control meansresponsive to current through said contacts for varying the length ofsaid opening stroke in accordance with the magnitude of said current,said current-responsive control means causing the length of said openingstroke to be greater for light-current interruptions than for heavycurrent interruptions, thus providing a stroke of greater length forcapacitance switching operations than for short circuit currentinterruptions.
 3. A vacuum-type circuit interrupter as defined in claim2 in which said stroke-length control means comprises: a. a first stopthat is normally disabled but which is effective upon removal of saiddisability to limit said opening stroke to a relatively short value, b.a second stop that limits said opening stroke to a greater length whensaid first stop is disabled, c. and current-sensitive means for removingsaid disability when the current through said contacts exceeds apredetermined value, thereby rendering said first stop effective togovern the stroke length on short circuit current interruptions.
 4. In apolyphase vacuum circuit breaker comprising a plurality of vacuuminterrupters for the respective phases of the circuit, each vacuuminterrupter comprising: a. a highly evacuated housing, b. a pair ofrelatively movable contacts within said housing that have a position ofengagement, c. an operating member projecting into said housing from theexterior thereof and coupled to one of said contacts, d. meanscomprising said operating member for moving said one contact through anopening stroke that separates said contacts and interrupts the circuittherethrough, e. a flexible metal bellows providing a vacuumtight sealbetween said operating member and said housing, f. and stroke-lengthcontrol means responsive to current through said contacts for varyingthe length of said opening stroke in accordance with the magnitude ofsaid current, the stroke-length control means of each phase beingoperable independently of the stroke-length control means of the otherphases for varying the stroke length of the interrupter in any one phasein accordance with the current in that phase without affecting thestroke length in the other phases.
 5. In a polyphase vacuum circuitbreaker comprising a plurality of vacuum interrupters for the respectivephases of the circuit, each vacuum interrupter comprising: a. a highlyevacuated housing, b. a pair of relatively movable contacts within saidhousing that have a position of engagement, c. an operating memberprojecting into said housing from the exterior thereof and coupled toone of said contacts, d. means comprising said operating member formoving said one contact through an opening stroke that separates saidcontacts and interrupts the circuit therethrough, e. a flexible metalbellows providing a vacuumtight seal between said operating member andsaid housing, f. and stroke-length control means responsive to currentthrough said contacts for varying the length of said opening stroke inaccordance with the magnitude of said current; the combination of: g. alinkage connected to the interrupters in all phases for impartingclosing motion thereto after an opening operation, h. latching means forholding said linkage in an operated position after a closing operationto hold said interrupters closed, i. said latching means beingreleasable to permit opening of said interrupters, j. a plurality ofopening operators respectively biasing the interrupters toward openposition and operable upon release of said latching means to separatethe contacts of their respective interrupters, and k. a lost-motionconnection between said linkage and each interrupter which allows theopening stroke in the associated interrupter to be terminated at arelatively short value by said stroke-length control means withoutblocking continued opening travel in the other interrupters.